Cleaning method and plasma processing apparatus

The present application is a U.S. National Stage Entry of International Patent Application No. PCT/JP2022/011196, filed Mar. 14, 2022, which claims the benefit of priority to Japanese Patent Application No. 2021-054055, filed Mar. 26, 2021, each of which is hereby incorporated herein by reference in its entirety.

The present disclosure relates to a cleaning method and a plasma processing apparatus.

Patent Document 1 proposes a technique in which the interior of a processing container is cleaned at a first pressure and a second pressure higher than the first pressure when the cleaning is performed by generating plasma while supplying a cleaning gas into the processing container.

The present disclosure provides a technique that suppresses damage to the interior of a processing container due to plasma cleaning and improves productivity.

A cleaning method according to an aspect of the present disclosure includes a specifying process and a cleaning process. In the specifying process, the pressure within a processing container during plasma cleaning is specified from the amount of damage to a protective film provided on the inner surface of the processing container and the cleaning rate at which a deposit deposited in the processing container is removed, wherein the amount of damage and the cleaning rate are conditions for plasma cleaning. In the cleaning process, the pressure within the processing container is adjusted to the pressure specified in the specifying process while supplying a cleaning gas into the processing container, plasma is generated in the processing container by microwaves, and the interior of the processing container is cleaned with the plasma.

According to the present disclosure, it is possible to suppress damage to the interior of a processing container due to plasma cleaning and to improve productivity.

Hereinafter, embodiments of a cleaning method and a plasma processing apparatus disclosed herein will be described in detail with reference to the drawings. The disclosed cleaning method and plasma processing apparatus are not limited by the embodiments.

In recent years, with the increasing density and miniaturization of semiconductor products, a plasma processing apparatus using microwaves for film formation is used in a semiconductor product manufacturing process. The plasma processing apparatus may generate plasma stably even in a high-vacuum state having a relatively low pressure by using microwaves. In addition, the plasma processing apparatus may generate high-density plasma by using microwaves. In the plasma processing apparatus, when film formation is performed, deposits are deposited on the surfaces of the structures within the processing container, such as the inner wall surface within the processing container. Therefore, in the plasma processing apparatus, a plasma cleaning is performed to remove deposits by causing a cleaning gas to flow into the processing chamber each time a film formation is performed on a predetermined number of substrates or each time a film formation is performed to a predetermined cumulative film thickness. For example, in Patent Document 1, a plasma cleaning is performed by switching the pressure within the processing container between two states of a first pressure and a second pressure higher than the first pressure.

It is known that a plasma processing apparatus is provided with a protective film on the inner surface of the processing container thereof in order to protect the inner surface of the processing container from plasma damage. In the processing container provided with a protective film, for example, in the cleaning such as that disclosed in Patent Document 1, in particular, plasma cleaning damage by the first pressure (low pressure) is great, and the frequency of maintenance, such as replacement of components, increases. Increased frequency of maintenance has a great effect on productivity. Therefore, there is a need for a technique for suppressing damage to the interior of the processing container due to plasma cleaning and improving productivity.

An embodiment will be described. First, an example of a plasma processing apparatus for executing a cleaning method of the present disclosure will be described.is a cross-sectional view schematically illustrating an example of a plasma processing apparatusaccording to an embodiment. The plasma processing apparatusillustrated inincludes a processing container, a stage, a gas supply mechanism, an exhaust mechanism, a microwave plasma source, and a controller.

The processing containeraccommodates a substrate W such as a semiconductor wafer. The processing containeris provided with a stagetherein. A substrate Wis placed on the stage. The gas supply mechanismsupplies gas into the processing container. The interior of the processing containeris exhausted by the exhaust mechanism. The microwave plasma sourcegenerates microwaves for generating plasma in the processing containerand introduces the microwaves into the processing container. The controllercontrols the operation of each part of the plasma processing apparatus.

The processing containeris formed of, for example, a metal material, such as aluminum or an alloy thereof, and has a substantially cylindrical shape. The processing containerincludes a plate-shaped ceiling wall, a bottom wall, and a side wall portionconnecting the ceiling walland the bottom wallto each other. The inner wall of the processing containermay be provided with a protective film by being coated with yttria (YO) or the like. The microwave plasma sourceis provided above the processing containerand introduces electromagnetic waves (microwaves) into the processing containerto generate plasma. The microwave plasma sourcewill be described in detail later.

The ceiling wallincludes a plurality of openings into which microwave radiation mechanismsand gas introduction nozzles(to be described later) of the microwave plasma sourceare fitted. The side wall portionhas a carry-in/out portfor performing carry-in/out of a substrate W to/from a transport chamber (not illustrated) adjacent to the processing container. In addition, the side wall portionis provided with gas introduction nozzlesat positions above the stage. The carry-in/out portis opened/closed by a gate valve.

An opening is provided in the bottom wall, and an exhaust mechanismis provided via an exhaust pipeconnected to the opening. The exhaust mechanismincludes a vacuum pump and a pressure control valve. By the vacuum pump of the exhaust mechanism, the interior of the processing containeris exhausted through the exhaust pipe. The pressure within the processing containeris controlled by the pressure control valve of the exhaust mechanism.

The stagehas a disk shape. The stageis made of a metal material, such as aluminum having an anodized surface, or a ceramic material, such as aluminum nitride (AlN). A substrate W is placed on the top surface of the stage. The stageis supported by a cylindrical support membermade of ceramic, such as AlN, and extending upward from the center of the bottom of the processing containerand a base member. A guide ringconfigured to guide the substrate W is provided on the outer edge of the stage. Inside the stage, lifting pins (not illustrated) configured to raise and lower the substrate W are provided to be capable of protruding and retracting with respect to the top surface of the stage.

Furthermore, the stagehas a resistance heating-type heaterembedded therein. The heaterheats the substrate W placed on the stageby being fed with power from a heater power supply. A thermocouple (not illustrated) is inserted into the stageso that the heating temperature of the substrate W can be controlled based on a signal from the thermocouple. In addition, the stageincludes an electrodehaving the same size as the substrate W and embedded above the heater. A radio-frequency bias power supplyis electrically connected to the electrode. The radio-frequency bias power supplyapplies radio-frequency bias for attracting ions to the stage. The radio-frequency bias power supplymay not be provided depending on a plasma processing characteristic.

The gas supply mechanismsupplies various processing gases into the processing container. The gas supply mechanismincludes gas introduction nozzlesand, gas supply pipesand, and a gas supplier. The gas introduction nozzlesare fitted into respective openings formed in the ceiling wallof the processing container. The gas introduction nozzlesare fitted into respective openings formed in the side wall portionof the processing container. The gas supplieris connected to each gas introduction nozzlevia the gas supply pipe. In addition, the gas supplieris connected to respective gas introduction nozzlesvia the gas supply pipes. The gas supplierincludes various gas sources. In addition, the gas supplieris provided with an opening/closing valve for performing starting and stopping the supply of various gases and a flow rate adjuster configured to adjust the flow rate of a gas. For example, when performing a film formation, the gas suppliersupplies a processing gas containing a film forming material. In addition, when performing a plasma cleaning, the gas suppliersupplies a cleaning gas.

The microwave plasma sourceis provided in an upper portion of the processing container. The microwave introduction device microwave plasma sourceintroduces electromagnetic waves (microwaves) into the processing containerto generate plasma.

The microwave plasma sourceincludes the ceiling wallof the processing container, a microwave output part, and an antenna unit. The ceiling wallfunctions as a ceiling plate of the processing container. The microwave output partgenerates microwaves and distributes and outputs the microwaves to a plurality of paths. The antenna unitintroduces the microwaves output from the microwave output partinto the processing container.

The microwave output partincludes a microwave power supply, a microwave oscillator, an amplifier, and a distributor. The microwave oscillator is solid state and oscillates microwaves at, for example, 860 MHz (e.g., PLL oscillation). The frequency of microwaves is not limited to 860 MHz, and a frequency in the range of 700 MHz to 10 GHz, such as 2.45 GHz, 8.35 GHz, 5.8 GHz, or 1.98 GHz, may be used. The amplifier amplifies the microwaves oscillated by the microwave oscillator. The distributor distributes the microwaves amplified by the amplifier to a plurality of paths. The distributor distributes microwaves while matching the impedance on the input and output sides.

The antenna unitincludes a plurality of antenna modules.illustrates three antenna modules of the antenna unit. Each antenna module includes an amplifierand a microwave radiation mechanism. The microwave output partgenerates microwaves, and distributes and outputs the microwaves to each antenna module. The amplifierof the antenna module mainly amplifies the distributed microwaves and outputs the amplified microwaves to the microwave radiation mechanism. The microwave radiation mechanismis provided on the ceiling wall. The microwave radiation mechanismradiates the microwaves output from the amplifierinto the processing container.

The amplifierincludes a phase shifter, a variable gain amplifier, a main amplifier, and an isolator. The phase shifter changes the phase of the microwaves. The variable gain amplifier adjusts the power level of the microwaves input to the main amplifier. The main amplifier is configured as a solid state amplifier. The isolator separates reflected microwaves that are reflected by the antennas of the microwave radiation mechanisms(to be described later) and headed toward the main amplifier.

As illustrated in, a plurality of microwave radiation mechanismsare provided on the ceiling wall. In addition, the microwave radiation mechanismseach have a cylindrical outer conductor and an inner conductor provided coaxially with the outer conductor within the outer conductor. In addition, the microwave radiation mechanismseach have a coaxial tube having a microwave transmission path between the outer conductor and the inner conductor, and an antenna that radiates microwaves into the processing container. On the bottom surface side of the antenna unit, a microwave transmission platefitted into the ceiling wallis provided. The bottom surface of the microwave transmission plateis exposed to the inner space of the processing container. The microwaves transmitted through the microwave transmitting plategenerate plasma in the space within the processing container.

is a view illustrating an example of an arrangement of antenna modules in a ceiling wallaccording to an embodiment. As illustrated in, seven microwave radiation mechanismsof the antenna module are provided on the ceiling wall. The microwave radiation mechanismsare arranged so that six of them are vertices of a regular hexagon, and one is arranged at the center of the regular hexagon. In addition, on the ceiling wall, microwave transmission platesare disposed corresponding to the seven microwave radiation mechanisms, respectively. These seven microwave transmission platesare arranged such that adjacent microwave transmission platesare equally spaced apart from each other. In addition, the plurality of gas introduction nozzlesof the gas supply mechanismare arranged to surround the periphery of the central microwave transmission plate. In addition, the number of antenna modules provided in the ceiling wallis not limited to seven.

The antenna unitaccording to the embodiment is configured to be capable of adjusting the power of microwave plasma radiated from the microwave radiation mechanismof each antenna module by controlling the amplifierof each antenna module. The antenna unitis configured to be capable of controlling the power ratio of microwave plasma radiated from the microwave radiation mechanismsbetween the central portion and the peripheral portion. For example, the antenna unitis capable of controlling the power ratio of microwaves between the central portion and the peripheral portion to be in the range of 0:550 to 500:550.

As long as a microwave power density can be appropriately controlled, a microwave plasma source having a single microwave introduction part having a size corresponding to a substrate W may be used.

The operation of plasma processing apparatusconfigured as described above is comprehensively controlled by the controller. A user interfaceand a storageare connected to the controller.

The user interfacemay be configured as an operation part, such as a keyboard, on which a process manager inputs commands to manage the plasma processing apparatus, or a display part, such as a display that visualizes and displays the operating state of the plasma processing apparatus. The user interfaceaccepts various operations. For example, the user interfaceaccepts a predetermined operation instructing the start of plasma processing.

The storageis a storage device that stores various types of data. For example, the storageis a storage device such as a hard disk, a solid state drive (SSD), or an optical disk. The storagemay be a semiconductor memory that is capable of rewriting data, such as a random access memory (RAM), a flash memory, or a nonvolatile static random access memory (NVSRAM).

The storagestores an operating system (OS) and various recipes executed by the controller. For example, the storagestores various recipes including recipes for executing each process of a cleaning method to be described later. In addition, the storagestores various data to be used in recipes. For example, the storagestores first relation data, second relation data, and cleaning setting data. Details of the first relation dataand the second relation datawill be described later. The cleaning setting datais data storing various settings for plasma cleaning. In addition, the programs or the data may be used in the state of being stored in a computer-readable computer storage medium (e.g., a hard disk, a CD, a flexible disk, or a semiconductor memory). Alternatively, the programs or data may be transmitted from another device at any time via, for example, a dedicated line to be used online.

The controlleris a device that controls the plasma processing apparatus. As the controller, an electronic circuit, such as a central processing unit (CPU) or a micro-processing unit (MPU), or an integrated circuit, such as an application-specific integrated circuit (ASIC) or a field programmable gate array (FPGA), may be adopted. The controllerhas an internal memory for storing programs and control data that define various processing procedures, and executes various processes using these programs or data. The controllerserves as various processors by executing various programs. For example, the controllerincludes an acceptor, a specifier, and a cleaning controller.

The controllercontrols each part of the plasma processing apparatus. For example, the controllercontrols each part of the plasma processing apparatusto perform film formation according to the recipe of recipe data stored in the storage. In the plasma processing apparatus, a substrate W is placed on the stage. The plasma processing apparatusperforms film formation on the substrate W placed on the stage. For example, the plasma processing apparatusapplies bias power to the stagefrom the radio-frequency bias power supply. In addition, the plasma processing apparatusforms a silicon-containing film on the substrate W by generating plasma by introducing microwaves into the processing containerfrom the microwave plasma sourcewhile suppling a processing gas containing, for example, a silicon-containing gas and a nitrogen-containing gas from the gas supplierinto the processing chamber.

Examples of the silicon-containing gas include a silane-based hydrogen gas or a silane-based halogen gas, such as SiH, SiH, or SiHCl. Examples of the nitrogen-containing gas include a hydrogen nitride-based gas, such as NH, NH, or NH, such as ammonia, hydrazine, or triazane, and nitrogen gas Nalone. In addition, the gas suppliermay further supply another gas, such as a rare gas or a carbon-containing gas, as a processing gas.

In the present embodiment, a SiN film is formed on the substrate W as a silicon-containing film by using, for example, SiHgas as the silicon-containing gas and NHgas as the nitrogen-containing gas.

The controllercontrols the power of microwave plasma radiated from the microwave radiation mechanismof each antenna module by controlling the amplifierof each antenna module during film formation. For example, the controllercontrols the power ratio of microwaves between the central portion of the upper portion of the processing chamberand the peripheral portion surrounding the central portion to be in the range of 0:550 to 500:550, as needed.

As described above, when the plasma processing apparatusperforms film formation, deposits are deposited on the surfaces of the structures within the processing container. For example, when a silicon-containing film is formed on a substrate W, the silicon-containing material is deposited as a deposit on the surfaces of the structures within the processing chamber. Examples of silicon-containing materials to be deposited include SiN, SiCN, SiON, SiOCN, SiC, and amorphous silicon (a-Si). In addition, as a deposit, amorphous carbon (a-C) may be deposited.

Therefore, the plasma processing apparatusexecutes plasma cleaning for removing deposits by generating plasma while causing a cleaning gas to flow into the processing chambereach time the film formation is performed on a predetermined number of substrates W or each time the film formation is performed to a predetermined cumulative film thickness. The plasma cleaning is executed by switching the pressure within the processing containerbetween two states during the cleaning, for example, as in the related arts.

When the plasma cleaning is executed, the protective film provided on the inner surface of the processing containeris damaged by the plasma for the plasma cleaning. In the plasma processing apparatus, when the plasma cleaning is repeatedly executed, the protective film on the inner surface of the processing containeris gradually etched by the plasma for the plasma cleaning, and the inner surface of the processing containeris exposed.

are views illustrating an example in which a protective film of a processing containeraccording to an embodiment is etched by plasma for plasma cleaning.schematically illustrates an upper portion of the processing containerin the initial state.schematically illustrates an upper portion of the processing containerthat has been subjected to repeated plasma cleaning. On the ceiling wallof the processing container, three microwave transmission platesprovided corresponding to the microwave radiation mechanismsare illustrated. A protective filmis provided on the inner surface of the processing container. The protective filmis, for example, an yttria (YO) film. In the plasma cleaning, plasma is generated in the space within the processing containerby microwaves radiated from the microwave radiation mechanismsand transmitted through the microwave transmission plates. In the plasma processing apparatus, when the plasma cleaning is regularly and repeatedly executed, the protective filmon the inner surface of the processing containeris etched by plasma and the inner surface of the processing containeris exposed. In, portions of the protective filmaround the microwave transmission platesare missing, and the inner surface of the processing chamberis partially exposed.

In the plasma cleaning, when the pressure within the processing containerduring the cleaning is low, the protective filmis damaged so much that the protective filmis etched and the inner surface of the processing containeris exposed. In addition, when the pressure within the processing containerduring the cleaning is high, the damage to the protective filmis small, and the etching of the protective filmis suppressed, but the cleaning time is prolonged, adversely affecting productivity.

The damage in the processing containerand the removal amount (cleaning rate) of deposits accumulated in the processing containerwill be further described.is a graph showing an example of the relationship between a pressure within a processing containerand the amount of damage to a protective filmin the plasma cleaning according to an embodiment. When the protective filmis etched, components of the protective filmscatter into the processing container. The vertical axis of the graph inrepresents the amount of damage Y to the protective film, in which the amount of damage Y increases toward the top side. The horizontal axis of the graph represents the pressure within the processing containerin the plasma cleaning, and the pressure increases toward the right side. The amount of damage to the protective filmis the amount of a component of the protective film deposited on the substrate W, in which the amount was obtained by executing plasma cleaning on the substrate W placed on the top surface of the stageand then taking out the substrate W. In the present embodiment, the area density per unit area of Y (yttrium), which is a component of yttria (YO) coated as the protective film, is expressed as the amount of damage Y.

As shown in, the amount of damage Y decreases as the pressure in the processing containerincreases. In addition, the decreasing tendency of the amount of damage Y decreases exponentially up to a certain pressure. That is, when the pressure within the processing containeris low, the amount of damage Y is large, and when the pressure within the processing containeris high, the amount of damage Y is small.

is a graph showing an example of the relationship between a pressure within a processing containerand a cleaning rate in plasma cleaning according to an embodiment. The vertical axis of the graph ofrepresents the cleaning rate of plasma cleaning, and the cleaning rate increases toward the top side. The horizontal axis of the graph represents the pressure within the processing containerin the plasma cleaning, and the pressure increases toward the right side. The cleaning rate is an amount of decrease per unit time in the film thickness of deposits within the processing containerby the plasma cleaning. In the present embodiment, the cleaning rate was obtained from a change in the spectrum of a specific element after measuring emission spectra by an optical sensor installed in the processing containerwhen removing deposits by the plasma cleaning.

As shown in, the cleaning rate decreases as the pressure within the processing containerincreases.

Return to. As described above, the storagestores the relationships of the amount of damage, the cleaning rate, and the pressure as first relation dataand second relation data.

The first relation datais data representing the relationship between the pressure within the processing containerand the amount of damage to the protective filmin the plasma cleaning. The first relation datamay be an expression representing, for example, the correlation between the pressure within the processing containerand the amount of damage as shown in. In addition, the first relation datamay be table data in which the pressure within the processing containeris stored for each amount of damage.

The second relation datais data representing the relationship between the pressure within the processing containerand the cleaning rate in plasma cleaning. The second relation datamay be an expression representing, for example, the correlation between the pressure within the processing containerand the cleaning rate as shown in. In addition, the second relation datamay be table data in which the pressure within the processing containeris stored for each cleaning rate.

The acceptordisplays various operation screens on the user interfaceand accepts various inputs. For example, the acceptoraccepts inputs of the amount of damage to the protective filmand the cleaning rate, which are conditions for plasma cleaning. In the present embodiment, the acceptoraccepts the inputs of the damage amount and the cleaning rate of the protective film, but is not limited thereto. The amount of damage and the cleaning rate of the protective filmas conditions for plasma cleaning may be included in recipe data for plasma cleaning, or may be received from another device.

From the amount of damage to the protective filmand the cleaning rate, which are conditions for plasma cleaning, the specifierspecifies the pressure within the processing containerduring the plasma cleaning. For example, from the first relation data, the specifierspecifies a first pressure range in which the amount of damage equal to or less than the amount of damage as the condition for the plasma cleaning is obtained. In addition, from the second relation data, the specifierspecifies a second pressure range in which a cleaning rate equal to or higher than the cleaning rate as the condition for the plasma cleaning is obtained. Furthermore, the specifierspecifies an overlap range where the specified first pressure range and second pressure range overlap each other.